Mastitis is the inflammation of the mammary gland caused by microorganisms that invade one or more quadrants of the bovine udder, multiply, and produce toxins that are harmful to the mammary gland. Economic loss to mastitis in the United States is estimated to be over $2 billion. This is approximately 10% of the total value of farm milk sales, and about two-thirds of this loss is due to reduced milk production in subclinically infected cows.
In subclinical mastitis, there may be no visible signs of the disease, and diagnosis of subclinical mastitis may be performed by a somatic cell count (SCC) of the milk. The SCC is the number of leukocytes or white blood cells per volume of milk and is also used as an index of milk quality. It has also been recognized that there are multiple types of leukocytes, each with its own significance. In milk from a healthy animal, the predominant cell types are lymphocytes, followed by lesser numbers of neutrophils and macrophages. The percentages of each kind of cell rise and fall as part of the immune response to infection. Those percentages, “the milk leukocyte differential”, cell count represent the unique immune status of an individual quarter udder, at a specific point in time for better diagnosis of subclinical mastitis.
One method for detecting the milk leukocyte differential is using flow-cytometry, which is an expensive, sophisticated tool typically only found in top research laboratories and generally not practical for the farmer. Another method for detecting the milk leukocyte differential is the “manual milk differential smear” (MMDS), which is a difficult and time consuming procedure, and is subject to great variability, even when performed by highly trained laboratory technologists. Both flow-cytometry and MMDS present practical difficulties for field research or a barn environment.
U.S. Patent Application Publication No. 2009/0233329 to Rodriguez discloses a wedge microfluidic slide chamber for detecting mastitis or other diseases from a body fluid of a mammal, such as from cow's milk. The wedge-shaped chamber uses capillary action to fill the chamber with the sample as a “self-preparing wet smear” with a meta-chromatic stain. The wedge-shaped microscope slide with the stained sample may be analyzed by visual identification and direct observation or by imaging instruments using computer-enhanced digital camera images. Accordingly, mastitis may be detected more easily with such a self-preparing wet smear.
Milk collection techniques for such a slide, however, may be time consuming and/or difficult. Typically, a sample from each quadrant of the cow's udder may be collected in different containers and pipetted by an operator into the wedge-shaped slide chamber for further analysis, for example, by an imaging instrument or reader. Moreover, it may be desirable to pipette the sample into the self-preparing wet smear relatively soon before placing the microscope slide into the imaging instrument or reader. The liquid samples may be stored in separate containers prior to analysis, and the tracking and/or storage of such samples may present various challenges, for example, to track which sample came from which cow and from which quadrant of the cow.